diff --git a/include/loki/details/pddl/exceptions.hpp b/include/loki/details/pddl/exceptions.hpp
index 2c41668e..3b378a9c 100644
--- a/include/loki/details/pddl/exceptions.hpp
+++ b/include/loki/details/pddl/exceptions.hpp
@@ -186,6 +186,22 @@ class MultiDefinitionObjectError : public SemanticParserError
     MultiDefinitionObjectError(const std::string& name, const std::string& error_handler_output);
 };
 
+/* Function */
+
+class IllformedFunctionDefinitionMissingValue : public SemanticParserError
+{
+public:
+    IllformedFunctionDefinitionMissingValue(const FunctionSkeleton& function, const Function& values, const std::string& error_handler_output);
+};
+
+class IllformedFunctionDefinitionMultipleValues : public SemanticParserError
+{
+public:
+    IllformedFunctionDefinitionMultipleValues(const FunctionSkeleton& function_skeleton,
+                                              const Function& ground_function,
+                                              const std::string& error_handler_output);
+};
+
 /* Compatibility errors */
 class MismatchedDomainError : public SemanticParserError
 {
diff --git a/src/pddl/exceptions.cpp b/src/pddl/exceptions.cpp
index 8f078e4e..13e2a2c3 100644
--- a/src/pddl/exceptions.cpp
+++ b/src/pddl/exceptions.cpp
@@ -18,7 +18,9 @@
 #include "loki/details/pddl/exceptions.hpp"
 
 #include "loki/details/pddl/domain.hpp"
+#include "loki/details/pddl/function.hpp"
 #include "loki/details/pddl/function_skeleton.hpp"
+#include "loki/details/pddl/object.hpp"
 #include "loki/details/pddl/predicate.hpp"
 
 #include <string>
@@ -174,6 +176,24 @@ MultiDefinitionObjectError::MultiDefinitionObjectError(const std::string& name,
 {
 }
 
+/* Function*/
+IllformedFunctionDefinitionMissingValue::IllformedFunctionDefinitionMissingValue(const FunctionSkeleton& function_skeleton,
+                                                                                 const Function& values,
+                                                                                 const std::string& error_handler_output) :
+    SemanticParserError("The function with name \"" + function_skeleton->str() + "\n misses a value definition in the initial state for arguments \""
+                            + values->str() + "\".",
+                        error_handler_output)
+{
+}
+
+IllformedFunctionDefinitionMultipleValues::IllformedFunctionDefinitionMultipleValues(const FunctionSkeleton& function_skeleton,
+                                                                                     const Function& ground_function,
+                                                                                     const std::string& error_handler_output) :
+    SemanticParserError("The function with name \"" + function_skeleton->str() + "\n has multiple values defined for \"" + ground_function->str() + "\".",
+                        error_handler_output)
+{
+}
+
 /* Compatibility errors */
 MismatchedDomainError::MismatchedDomainError(const Domain& domain, const std::string& domain_name, const std::string& error_handler_output) :
     SemanticParserError("Mismatched domain names \"" + domain->get_name() + "!=" + domain_name + ".", error_handler_output)
diff --git a/src/pddl/parser.cpp b/src/pddl/parser.cpp
index 4f363fbc..65bf64d7 100644
--- a/src/pddl/parser.cpp
+++ b/src/pddl/parser.cpp
@@ -167,6 +167,7 @@ Problem parse(const ast::Problem& problem_node, Context& context, const Domain&
             std::visit(UnpackingVisitor(initial_literals, numeric_fluents), initial_element);
         }
     }
+
     /* Goal section */
     auto goal_condition = std::optional<Condition>();
     if (problem_node.goal.has_value())
diff --git a/src/pddl/parser/initial.cpp b/src/pddl/parser/initial.cpp
index 6256524d..1b586275 100644
--- a/src/pddl/parser/initial.cpp
+++ b/src/pddl/parser/initial.cpp
@@ -27,6 +27,9 @@ namespace loki
 
 std::vector<std::variant<GroundLiteral, NumericFluent>> parse(const ast::Initial& initial_node, Context& context)
 {
+    // TODO: IllformedFunctionDefinitionMissingValue and IllformedFunctionDefinitionMultipleValues using value_definitions.
+    std::unordered_map<FunctionSkeleton, std::unordered_set<Function>> value_definitions;
+
     auto initial_element_list = std::vector<std::variant<GroundLiteral, NumericFluent>>();
     for (const auto& initial_element : initial_node.initial_elements)
     {
diff --git a/tests/unit/pddl/factory.cpp b/tests/unit/pddl/factory.cpp
index f7021bcc..365301fe 100644
--- a/tests/unit/pddl/factory.cpp
+++ b/tests/unit/pddl/factory.cpp
@@ -18,6 +18,7 @@
 #include <gtest/gtest.h>
 #include <loki/details/pddl/factory.hpp>
 #include <loki/details/pddl/object.hpp>
+#include <loki/details/pddl/term.hpp>
 
 namespace loki::domain::tests
 {
@@ -54,4 +55,19 @@ TEST(LokiTests, FactoryIteratorEmptyTest)
     EXPECT_EQ(objects.size(), 0);
 }
 
+TEST(LokiTests, FactoryVariantTest)
+{
+    PDDLFactory<ObjectImpl> objects(2);
+    PDDLFactory<TermImpl> terms(2);
+    const auto object_0 = objects.get_or_create<ObjectImpl>("object_0", TypeList());
+    const auto object_1 = objects.get_or_create<ObjectImpl>("object_1", TypeList());
+
+    const auto term_0_object_0 = terms.get_or_create<TermObjectImpl>(object_0);
+    const auto term_1_object_0 = terms.get_or_create<TermObjectImpl>(object_0);
+    const auto term_2_object_1 = terms.get_or_create<TermObjectImpl>(object_1);
+
+    EXPECT_EQ(term_0_object_0, term_1_object_0);
+    EXPECT_NE(term_0_object_0, term_2_object_1);
+}
+
 }